Crystalline Volume Fraction Research Articles

Obtaining extremely low coercivity of high Bs FeCoBSiCPCu nanocrystalline alloys through modulation of magnetic anisotropy

Longitudinal magnetic field annealing is utilized for modifying the magnetic anisotropy and enhancing the magnetic softness of Fe75Co8(B10Si3C3P1)1-x/17Cux (x = 0.5, 0.75, 1, 1.25) nanocrystalline alloys. All of the magnetic field-annealed nanocrystalline alloys with Cu content more than 0.5 at.% exhibit significantly improved soft-magnetic properties, including high saturation magnetic flux density up to 1.87 T, effective permeability of 13,000–16,000 under the condition of 1 A/m and 1 kHz, coercivity as low as 1.6 A/m, and core loss of 0.11–0.45 W/kg under the condition of 1.0 T and 50 Hz. The application of a magnetic field promotes the nucleation and inhibits the growth of grains, leading to an increase in the number density of nanocrystals and the crystalline volume fraction, and a reduction in the grain size. The magnetic field annealing reduces the effective magneto-crystalline anisotropy energy to 2–4 J/m3, and induces longitudinal magnetic anisotropy with anisotropy energy density of 400–900 J/m3 which shows dependence on the crystalline volume fraction. The field-induced magnetic anisotropy dominates over the random local magnetic anisotropies, and results in the formation of regular magnetic domains aligned longitudinally, pinning-free domain wall displacement, and thus enhanced soft-magnetic properties.

Non-Isothermal Analysis of the Crystallization Kinetics of Amorphous Mg72Zn27Pt1 and Mg72Zn27Ag1 Alloys.

In this study, thin ribbons of amorphous Mg72Zn27Pt1 and Mg72Zn27Ag1 alloys with potential use in biomedicine were analyzed in terms of the crystallization mechanism. Non-isothermal annealing in differential scanning calorimetry (DSC) with five heating rates and X-ray diffraction (XRD) during heating were performed. Characteristic temperatures were determined, and the relative crystalline volume fraction was estimated. The activation energies were calculated using the Kissinger method and the Avrami exponent using the Jeziorny-Avrami model. The addition of platinum and silver shifts the onset of crystallization towards higher temperatures, but Pt has a greater impact. In each case, Eg > Ex > Ep (activation energy of the glass transition, the onset of crystallization, and the peak, respectively), which indicates a greater energy barrier during glass transition than crystallization. The highest activation energy was observed for Mg72Zn27Pt1 due to the difference in the size of the atoms of all alloy components. The crystallization in Mg72Zn27Ag1 occurs faster than in Mg72Zn27Pt1, and the alloy with Pt has higher (temporary) thermal stability. The Avrami exponent (n) values oscillate in the range of 1.7-2.6, which can be interpreted as one- and two-dimensional crystal growth with a constant/decreasing nucleation rate during the process. Moreover, the lower the heating rate, the higher the nucleation rate. The values of n for Mg72Zn27Pt1 indicate a greater number of nuclei and grains than for Mg72Zn27Ag1. The XRD tests indicate the presence of α-Mg and Mg12Zn13 for both Mg72Zn27Pt1 and Mg72Zn27Ag1, but the contribution of the Mg12Zn13 phase is greater for Mg72Zn27Ag1.

Effect of Laser Irradiation and Tensile Stress on Microstructure and Magnetic Properties of Fe-Based Amorphous Alloys.

The effect of laser irradiation and tensile stress on the microstructure and soft magnetic properties of the FeSiBNbCu nanocrystalline alloy prepared using a continuous laser has been investigated. The experimental results indicate that a decreased laser scanning speed provides more thermal energy to induce nanocrystals and encourage grain growth. When the scanning speed is excessively high, the crystallization process will cease due to a lack of energy to drive diffusion phase transitions. Nevertheless, the introduction of tensile stress could significantly promote crystallization in FeSiBNbCu alloy samples irradiated at these high laser scanning speeds. This phenomenon can be attributed to the augmentation of compressive thermal stress at the interface between the laser-treated track and the untreated region. This heightened compressive stress promotes the diffusivity of atoms, and, as a result, the transformation from amorphous to crystalline states can be enhanced. As the applied tensile stress increases, both grain size and crystalline volume fraction exhibit a proportional augmentation. Consequently, these changes manifest in the soft magnetic properties. The crystalline volume fraction can reach 62%, and the coercivity is 2.9 A/m at the optimized scanning speed; these values correspond to 54% and 3.3 A/m under specific tensile stress loading.

Magnetic properties and structure of short-term annealed FeCuBPSi nanocrystalline alloys

Alloys with composition Fe80−xCu1B11P4Si4+x (x = 0 and 4), i. e. with Si 4 at % or 8 at % have been prepared by rapid quenching from the melt in air. For comparison the alloy with P 3 at % and Si 8 at % has been investigated as well. As-quenched structure of all ribbons was checked by X-ray diffraction. Subsequently the samples were submitted to thermal analysis, scanning and transmission electron microscopy and magnetic measurements. Hysteresis loops of strips after short-term annealing at 400, 420 and 500 °C for 5 min changed their shape – the saturation magnetic polarization increased. Its value changed from 1.67 to 1.74 T depending of the crystalline volume fraction for Fe80Cu1B11P4Si4 alloy. Addition of Si to the studied P 4 at % alloy leads to a decrease of coercivity after short-term annealing at the temperatures below the onset of the first transformation. Magnetic work decreased several times and its orientation acquired the distinct orientation along the ribbon axis.

Highly conductive p-type nc-SiOX:H thin films deposited at 130°C via efficient incorporation of plasma synthesized silicon nanocrystals and their application in SHJ solar cells

We present highly conductive and transparent p-type hydrogenated nanocrystalline silicon oxide (p-type nc-SiOX:H) layers produced by Plasma Enhanced Chemical Vapor Deposition (PECVD) at 130°C and 150°C. We report on the crystalline volume fraction (XC), spectral broadening parameter C, and dark conductivity (σ) as functions of the growth temperature and RF power, and how these properties evolve with post-deposition annealing at 250°C and 300°C. Interestingly, we observe that the best layers in terms of crystalline volume fraction and conductivity are obtained at the lowest temperature and RF power, which we attribute to the soft landing of silicon nanocrystals synthesized in the plasma. The p-type nc-SiOX:H layers with the best properties on glass substrates are implemented as carrier-selective contacts in silicon heterojunction (SHJ) solar cells with the structure: (n) a-Si:H / (i) a-Si:H / n-type c-Si / (i) a-Si:H / (i) a-SiOX:H / (p) nc-SiOX:H / (p) nc-Si:H where all films are deposited by PECVD. The cells were completed with sputtered ITO on the front and rear sides plus Ag on the rear side, and Ag grid on the front, with the best devices showing conversion efficiencies of 21.8%, which, contrary to a-Si:H contact layers, are preserved or even slightly improved upon annealing at 240°C.

Optimization of electromagnetic properties for soft magnetic powder cores prepared by gas-atomized FeSiBCuNb powders with continuously distributed the phase structures

The FeSiBCuNb gas-atomized powders (GAPs) show high sphericity, which is conducive to the formation of uniform insulating coating layers. However, it is difficult to obtain completely amorphous GAPs with relatively large particle sizes for Fe-based nanocrystalline alloys. In this work, the raw FeSiBCuNb GAPs with continuously distributed the phase structures are used to prepare soft magnetic powder cores (SMPCs). The effects of annealing process parameters on the average grain size, crystalline volume fraction, magnetic anisotropy constant (K), residual internal stress and magnetic properties of the SMPCs were studied in detail. The results showed that the increase of annealing temperature was more helpful for the magnetic properties of the SMPCs than extension of annealing time, which was due to average magnetic anisotropy constant (〈K〉) on coercivity primarily influenced on the SMPCs under the different annealing temperatures. When the annealing temperature is 500 °C, heating time is 50 min and holding time is 10 min, the NSMCs achieve relatively excellent magnetic properties: the effective permeability is 29.38 at 100 kHz, the quality factor is 126, the losses are 786 mW/cm3 (20 mT, 1 MHz), and the DC-bias characteristic is 67.28% (100 Oe or 7960 A/m). These results provided the potential for utilization of the raw FeSiBCuNb GAPs with continuously distributed the phase structures.

A generalized analytical model for predicting the elastic properties of fibrovascular bundles using Crystal-Fibril-Bundle approach

In order to understand how the structural parameters of vegetable fibers influence their elastic modulus; a generalized analytical model was developed. The model, the Crystal-Fibril-Bundle theory, includes the three main factors that influence the modulus of elasticity of the fiber bundle; the microfibril angle, percentage crystallinity and cell wall volume fraction. The model is generalized and acts as a top-down and bottom-up approach that can be used to predict the modulus of any hierarchical level in any vegetable fibers. The model was verified experimentally using sisal, abaca, banana and date palm fibers, and the model results showed very high agreement with the experimental results (<10 % deviation). Further, a parametric study was conducted to simulate the effect of each structural parameter on the bundle modulus of elasticity. The Crystal-Fibril-Bundle approach provides a novel and insightful tool to understand the knockdown in elastic properties resulting from the bottom-up transition through the structural hierarchical levels of vegetable fiber. It can help natural fiber researchers estimate the fibers elastic performance without the need for intensive testing. It also helps natural fiber composite designers in developing sustainable composites with enhanced performance. This model is considered the first exhaustive model to encompass all the major structural parameters in a single model.

Surface modifications of TiO2 nanostructured materials induced by 120 MeV Ag ions

The effect of swift heavy ion irradiation on structural, optical, and microstructural properties of TiO2 has been studied. Pellets prepared from TiO2 nanoparticles have been irradiated by 120 MeV Ag ions at different fluences ranging from 5 × 1011 to 1 × 1013 ions cm−2. X‐ray diffraction (XRD), Raman, UV–visible, and photoluminescence (PL) studies indicated anatase phase both in as‐prepared and irradiated pellets. XRD study revealed the crystallite size of the particles as ~16 nm, which is close to the upper limit of the particle size where anatase phase is most stable. Our study thus established the importance of the initial microstructure on the irradiation response of the nanoparticles. Though irradiation did not affect the crystal structure and the polycrystalline nature of the anatase TiO2, it suppressed the crystalline volume fraction. Poisson fitting of the suppression of XRD peak area with irradiation fluence revealed radius of the track of each 120 MeV Ag ion in TiO2 nanoparticles as ~2.1 nm. Irradiation, in addition to creating disorder, darkened the surface of the pellets because of the creation of oxygen vacancies in the TiO6 octahedra. Reorganization of these defects led to suppression of the band gap of TiO2 nanoparticles from 3.19 eV of the pristine sample to 3 eV for samples irradiated beyond a critical fluences 3 × 1012 ions cm−2. The size of the nanoparticles and their agglomeration remained unaffected by irradiation as indicated by field emission scanning electron micrographs.

Discussion on Factors Affecting Dyeing of Bio-based Polyamide 5,6 Fibers Compared with Polyamide 6,6 Fibers

To replace petroleum-based nylon and broaden the applications of polyamide 5,6 (PA56) in textiles, it is necessary to investigate the factors affecting the dyeing of bio-based PA56. In this work, bio-based PA56 and polyamide 6,6 (PA66) fibers were dyed with an acid dye. A comprehensive comparison of the factors affecting the dyeing performance of the PA56 and the PA66 fibers was carried out by measurements of the end-group content, crystallinity, and free volume fraction. The free volume fractions of the fibers in the dyeing process were calculated by the Williams-Landel-Ferry equation. Compared to the PA66 fibers, the results showed that the PA56 fibers had a better dyeing performance and water absorption behavior. Under the conventional dyeing process with water, the free volume fraction of PA56 fibers was slightly larger than that of the PA66 fibers. The larger the free volume, the more space for segmental motion and the easily entering of the dye into the interior of a fiber. The crystallinity of the PA56 fibers was 26.9%, which was lower than the 35.6% of the PA66 fibers. The lower crystallinity of the PA56 fibers means less regularity of macromolecular arrangement. The end-amino groups of the PA56 fibers and the PA66 fibers were 39.6 mmol/kg and 44.7 mmol/kg, respectively. Since the -NH2 groups only existed on the end of the polymer chains and the amount of -NH2 groups was low, the effect of the -NH2 groups content on the dyeing results was very small. Taking all these factors into consideration, the lower arrangement and the better segmental mobility of the molecular chains in the amorphous areas gave rise to the better dyeing performance of the PA56 fibers.

Micromechanical modelling of biodegradable semi-crystalline polymers: The evolution of anisotropic mechanical properties during degradation

The mechanical properties of biodegradable polymers are strongly linked to molecular weight and crystallinity. In this study, our modelling approach is used to relate changes in physical properties (molecular weight, crystalline volume fraction and porosity) of a semi-crystalline PLLA during degradation to macroscopic mechanical properties (modulus). We create a database of mechanical behaviour based on possible values of these properties, which is then queried to quickly predict the modulus without the need for multiscale approaches. Initially, the semi-crystalline polymer is considered as an ensemble of crystalline amorphous regions with no preferential direction. In subsequent simulations, the effect of anisotropy is investigated by considering various orientations and dispersions of the crystalline phase. Theoretical bounds were calculated and compared to simulations and published data. The database of mechanical behaviour was modified to capture the emergence of porosity during degradation. These predictions are compared against previously published experimental values of Young’s modulus for PLLA (Poly (L-lactide)) during degradation with good agreement. These simulations also provide insight into the transition to brittle behaviour during degradation.

The mechanical performance of optically tuned ceramic nanomultilayers

Multifunctional optical nanomultilayers (NMs) are needed for a wide array of applications, ranging from optical windows to electronic screens. Since the individual material constituents in optical coatings are often selected only for their desirable optical properties, mechanical characterization of the optical nanomultilayers is typically limited. Here, AlN/SiO2, TiO2/SiO2, and AlN/Al2O3 nanomultilayers synthesized in non-optimized and optimized optical performance layer configurations are tested using microtensile, nanoindentation, and pillar splitting techniques to highlight the effects of optical optimization on mechanical performance. Trends within each type of test and across all deformation modes reveal that layer thickness, volume fraction, and interfacial crystallinity can be viewed as controlling features for optical and mechanical performance, although their correlation may vary. It was observed that both configurations of the AlN/Al2O3 NMs exhibit the highest mechanical performance across all three testing techniques with an average experimental transmittance of 93.8% for the optimized layer configuration. Overall, the results from this expanded view of mechanical properties in ceramic optical nanomultilayers suggest the possibility of tuning film characteristics for joint optimization of opto-mechanical nanomultilayered coatings.

Structural analysis of graphene-capped copper by spectroscopic ellipsometry for humidity reliability assessment

The reliability of graphene-capped copper (Gr/Cu) against humidity is assessed by spectroscopic ellipsometry (SE). Changes in the volume fraction of crystalline Gr in single-layer graphene (SLG) and tri-layer graphene (TLG), and also Cu-oxide thicknesses under the Gr cap were characterized by SE before and after humidity reliability testing. It was found that TLG has a higher moisture resistance than SLG with less change in the crystalline Gr volume fraction and thickness than that of SLG, and this leads to the reduction in Cu-oxide thickness and the uniformity under the Gr cap. The results were consistent with the analysis results by X-ray photoelectron spectroscopy and Raman spectroscopy excluding variations due to differences in analysis areas of each method. Since detailed structural changes, such as Gr quality and thickness, can be evaluated non-destructively, SE is considered to be a promising method for the detailed analysis of Gr/Cu structures.

Effect of Manufacture-Induced Interfaces on the Tensile Properties of 3D Printed Polyamide and Short Carbon Fibre-Reinforced Polyamide Composites.

This study aims to elucidate the structure-property-process relationship of 3D printed polyamide and short carbon fibre-reinforced polyamide composites. The macroscopic properties (tensile modulus) of the 3D printed samples are quantitatively correlated to the printing process-induced intrinsic microstructure with multiple interfaces. The samples were printed with different layer thicknesses (0.1, 0.125 and 0.2 mm) to obtain the varied number of interface densities (number of interfaces per unit sample thickness). The result shows that the printed short carbon fibre-reinforced polyamide composites had inferior partially bonded interfaces compared to the printed polyamide, and consequently exhibited interface-dependent elastic performance. The tensile modulus of 3 mm thick composites decreased up to 18% as a function of interface density, whilst the other influencing aspects including porosity, crystallinity and fibre volume fraction (9%) were the same. Injection moulding was also employed to fabricate samples without induced interfaces, and their tensile properties were used as a benchmark. Predictions based on the shear-lag model were in close agreement (<5%) with the experimental data for the injection-moulded composites, whereas the tensile modulus of the printed composites was up to 38% lower than the predicted modulus due to the partial bonded interfaces.

The local crystallization thresholds under laser irradiation of the Cu+‐ion implanted Ge layers with various thicknesses

AbstractPorous Ge layers were fabricated by implanting Cu+ ions of various acceleration energies into c‐Ge substrate. This made it possible to form amorphous porous Ge layers of thicknesses from 18.6 to 50.5 nm. The distribution depth profiles of implanted Cu+ ions in Ge were simulated by SRIM‐2013 program. The formed layers were studied by Raman spectroscopy. The excitation was carried out by a laser with a wavelength of 488 nm, which has a small penetration depth of ∼20 nm. In the Raman spectra, there is a possibility to distinguish the contribution from the amorphous Ge film, the crystalline c‐Ge substrate, and Ge nanocrystals, which appear under intense laser excitation due to local crystallization. The decomposition of the spectra into individual components makes it possible to subtract the contribution of the substrate and estimate the crystalline volume fraction in the layers. The results obtained confirm the hypothesis of low thermal conductivity of the porous layer, due to which local crystallization occurs.

Enhanced corrosion resistance of a ZrCuNiAl bulk metallic glass in simulated groundwater by minor crystallization

Understanding the corrosion behaviors of bulk metallic glasses (BMGs) in practical working environment is essential for the applications of BMGs as corrosion resistance materials. The present work investigated the corrosion behaviors of Zr50.7Cu28Ni9Al12.3 (at. %) BMG and also its heat treated alloys with different volume fraction of crystalline phase in a solution simulating groundwater. It was shown that the corrosion of the present ZrCuNiAl alloy is induced by pit etching and Cu would be aggregated at the corrosion positions in a form of Cu2+ ions. Zr, Ni and Al would inversely be dissolved by the simulated groundwater and so were lack at the corrosion positions, and they are probed as form of Zr4+, Ni2+ and Al3+ ions on the corrosion surface, which supports the formation of metal oxides ZrO2, CuO, NiO and Al2O3. The experimental results discover a corrosion resistance trend first enhancing and then reducing with increasing crystalline phase volume fraction, proving that minor crystallization in fact also improve corrosion resistance in this BMG system, but large volume fraction of crystalline phases would deteriorate the anti-corrosion performance of BMGs. Thus the amorphous state itself improves corrosion resistance of the studied alloy.

Achievement of 25.54% power conversion efficiency by optimization of current losses at the front side of silicon heterojunction solar cells

AbstractParasitic absorption in the front window layers of transparent conductive oxide (TCO) films and carrier selective collection layers and the optical shading losses from the metallic finger grid mainly limit the current generation in silicon heterojunction (SHJ) solar cells. In this work, we demonstrate an improved short‐circuit current density (Jsc) of 40.24 mA/cm2 through a combination of novel window layers composed of transition metal doped indium oxide (IMO) and hydrogenated nanocrystalline silicon oxide (nc‐SiOx:H) films and Cu plating for SHJ solar cells. By introducing water vapor during direct current (DC) magnetron sputtering deposition process, IMO films show a large optical band gap (Eg) of about 3.88 eV and high mobility up to 83.2 cm2/V·s, while maintaining a low carrier concentration, which leads to high transparency and low near‐infrared (NIR) free carrier absorption (FCA). In addition to its high deposition rate and crystalline volume fraction, we found that nc‐SiOx:H films deposited by very high frequency (VHF) excited plasma‐enhanced chemical vapor deposition (PECVD) show an excellent surface passivation quality, which not only improves the open circuit voltage (Voc) of SHJ cells but also increases the Jsc through improved carrier selective collection. The quantified Jsc breakdown analysis was performed to identify the room for improvement, and it showed that the front shading loss (about 1.32 mA/cm2) is the largest portion. By combining the benefits of these window layer enhancements with the further use of fine line width and conductivity of Cu plating, SHJ solar cells, with a Jsc improvement of 0.57 mA/cm2 and a certified efficiency of 25.54%, were achieved on a total area of 274.5 cm2 using in‐house pilot production line equipment.

Resistance Drift Convergence and Inversion in Amorphous Phase Change Materials

AbstractPhase change materials (PCMs) are key to the development of artificial intelligence technologies such as high‐density memories and neuromorphic computing, thanks to their ability for multi‐level data storage through stepwise resistive encoding. Individual resistance levels are realized by adjusting the crystalline and amorphous volume fraction of the memory cell. However, the amorphous phase exhibits a drift in resistance over time that has so far hindered the commercial implementation of multi‐level storage schemes. In this study, the underlying physical process of resistance drift with the goal of modeling is elucidated that will help minimize and potentially overcome drift in PCM memory devices. Clear evidence is provided that the resistance drift is dominated by glass dynamics. Resistivity convergence and drift inversion for the amorphous chalcogenide Ge15Te85 and the PCM Ge3Sb6Te5 are experimentally demonstrated and these changes are successfully predicted with a glass dynamics model. This new insight into the resistance drift process provides tools for the development of advanced PCM devices.

Growth of high-crystallinity silicon films by a combination of intermittent pulse heating and plasma-enhanced chemical vapor deposition

We have developed a process to grow high-crystallinity silicon films on insulators by intermittent pulse heating (IPH)-assisted plasma-enhanced chemical vapor deposition to address a drawback of incubation layer formation at the early stage of growth. By applying electrical pulses (22 V, 5 Hz, 10% duty ratio) to a Mo strip underneath a SiO2 layer, the surface is instantaneously heated to 1050 K while maintaining a steady substrate temperature of 670 K. The growth mechanism similar to that of solid-phase epitaxy enhanced its growth rate up to 1.2 nm s−1, which is five times greater than that of a-Si grown outside the Mo strip. The grown films assisted with IPH also showed a 97% crystalline volume fraction with no incubation layer.

Sol-gel-derived transparent glass-ceramics for photonics

Photonic glass-ceramics are two-phase materials constituted by nanometer sized crystals, passive or activated by luminescent species, embedded in a glass matrix. Among the different techniques used to fabricate transparent glass ceramics the sol-gel route is highly appreciated because it allows to explore different compositions and develop novel functionalities. By engineering glass-ceramics chemistry, nature, or volume fractions of crystalline and amorphous phases, several interesting properties can be achieved and tailored so that the sol-gel technique appears one of the most versatile processes for the fabrication of photonic systems. The aim of the present paper is to give a brief state of the art and some significant examples of systems developed, even in our research network, during the last ten years of activity, in order to highlights the reliability and versatility of sol-gel -derived glass-ceramics for photonics application. With this aim, the main topics discussed here deal with: (i) transparent rare-earth-activated SiO2–SnO2 glass-ceramics; (ii) mechanical properties of glass ceramics coatings.

The Ga20Ge20Se60 glass-ceramics as a promising long-wave IR optical material

The Ga20Ge20Se60 chalcogenide glass-ceramics with a crystalline phase volume fraction of 50–55%, an average crystal size of 2–5 μm, and a transparency of 50–65% in the spectral range of 7–16 μm (at 2 mm sample thickness) are prepared. The features of phase formation during glass-forming melt quenching and subsequent annealing are studied. In samples quenched in water from 750 to 850 °C, Ga40-xGexSe60 (x = 20–30) solid solutions with a cubic unit cell are formed. Upon quenching from 700 °C, solid solutions isostructural to monoclinic Ga2Se3 are formed. Annealing of glass-ceramics at 480 °C leads to the decomposition of the cubic phase and the appearance of mixed GaGeSe3. Fracture toughness, elastic modulus, and abrasive resistance increase with increasing gallium content in GaxGe40-xSe60 (x = 5–20) samples. The reasons for the high transparency of Ga20Se20Se60 glass-ceramics in the long-wave infrared range and its dependence on the production conditions are established and discussed.